Method for interfitting machined parts



Aug. 4, 1953 M. 5. BLACK ET AL METHOD FOR INTERFITTING MACHINED PARTSFiled Feb. 28 1950 W J J 3nventors M/LLA RD 5. BLACK a M 7 k 6 r d R 5 AGttorneg Patented Aug. 4, 1953 METHOD FOR INTERFISTTING MACHINED ARTMillard s. Black, Huntington Park, and Albert G. Satterla, Jr.,Whittier, Califi, assignors to Fluid Packed Pump Company, Los Nietos,Calif., a

partnership Application February 28, 1950, Serial No. 146,764

11 Claims.

' This invention relates to a method for tightly interfitting machinedparts. For a better understandin of the present method, the pump barrel,such as in pumps conventionally employed in wells, will here provide thebasis in respect to which the method will be described. It should-beunderstood, however, that the barrel is intended as an exemplary device.

. For reasons of durability, pump barrels essentially comprise a jacketand a suitable number of sleeves or liners therein, the latter havingthe I required hardness to resist wear of the piston operating in thebarrel and also having the required resistance to corrosion.

At the present time there are two generally conventional methods forobtaining a tight fit of the liners in a barrel jacket. Both entailmachining of the outer diameter of the liners to a dimension slightlygreater than the machined internal diameter of the jacket. Since thebarrels and, therefore, the jackets are frequently fifteen feet long andseldom less than six feet long, and the liners have a length in thenature of ten to twelve inches, it will be evident that to attempt todrive or press the liners into the jacket would be unsatisfactory. Oneof the mentioned conventional methods entails heating the jacket to adegree sufiicient to cause the same to expand to a size freely admittinthe liners and then allowing the jacket to cool and shrink over theliners to tightly grip the same. The other conventional method entailssubjecting the liners to low temperatures to cause them to shrink to asize whereby they Will freely slip into the jacket. When the liners arerestored to normal temperatures, they will expand to their original sizeand tightly fit the jacket. Thus, in one case, the jacket is temporarilyexpanded, and in the other, the liners are temporarily shrunk orcontracted.

In both cases, unless the interference fit of the jacket and liners isinitially accurately gauged, the jacket is normally under considerablestress which is increased under working conditions wherein thetemperature of the barrel, due to friction and for other reasons, risesabove normal.

In contradistinction to, the above-described methods, the present methodentails effecting a tight interfit of liners in a jacket by subjectingthe entire assembly thereof to sub-zero temperatures to cause the linersto exp-and or grow to a size greater than theirinitial size, it being anobject of, the present invention to provide a method, as indicated, inwhich an entire assem bly is subjected to abnormal temperatures ratherthan subjecting one or the other components of the assembly to abnormaltemperatures, as in the old methods here given.

We have found that certain iron alloys have the property of growing whensubjected to sub-zero temperatures and that the growth is permanent.While other metals expand only under heat and then contract when theheat is dissipated, and contract temporarily when subjected to sub-zerotemperatures, iron alloys containing nickel and chromium permanentlygrow when subjected to sub-zero temperatures. After growth, such alloysare stabilized in the same manner as other metals, and return to thesize to which the same have grown after normal expansion and contractionas will other metals.

Accordingly, another object of the invention is to provide a method forproducing a tightly interfitted assembly of elements that makes use ofthe permanent growth characteristics of certain metals, thus enablinmachining of the elements for an initialfree orloose interfit whichbecomesv a tight interfit when the assembly is subjected to sub-zerotemperatures.

Of importance also is the fact that the hardness of alloys, asmentioned, increases after growth, a material advantage where suchincreased hardness is desired. Also of importance is that such alloysare highly corrosion-resistant.

Under tests which we have conducted, it has been found that 5% Ni and 2%Or with 93% Fe provides an alloy having desired properties with respectto hardness and resistance to corrosion. and that the same is easilymachineable. The given formula is suitable for producing barrel linersthat are approximately two inches in diameter and ten to twelve incheslong. Should less hardness and corrosion-resistance be satisfactory, thenickel content may vary between 3.5% and 4%, and the chromium between1.4% and. 1.6%.

Reference is now made to the drawing in which: i

Fig. 1 is an elevational view of a pump barrel, partly in longitudinalsection and partly broken away.

Fig. 2 is an enlarged longitudinal sectional view, showing the interfitof the parts before the assembly is subjected to sub-zero temperatures.

Fig. 3 is a similar View after application of cold.

In a conventional manner, the barrel that i illustrated comprises ametal jacket 5 towhich is fitted end connections 6, the latter affordingend shoulders. 1 between which a series of liners '8 reside within thejacket 5.

According to the present method, the length of the barrel betweenshoulders I is made to be somewhat larger than the total length of allof the liners 8 when the latter, after machining, are at normaltemperatures. In practice, it has been found that ten to twelve inchlong liners of an iron alloy, as above, will permanently elongate some.015 inch. Consequently, if there are ten liners 8 in the jacket, thetotal length of all of the liners is made to be some .150 inch less thanthe distance between shoulders I. Some variation is permissibleproviding the expanded total length of the liners closely approximatesthe distance between shoulders l to insure tight joints where the linersabut.

The internal diameter 9 of the jacket is machined to be slightly greaterthan the machined external diameter 10 of the liners. In practice, ithas been found that the liners expand or grow diametrally some .002 inchper one inch diameter, a two inch diameter liner, growing approximately.004 inch. Thus, if the external diameter of the liners is machined to adimension .002 inch smaller than the internal diameter of the jacket,the liners can readily be slipped, with suitable clearance, into thejacket, as suggested in Fig. 2, in which the clearance is exaggeratedfor illustrative purposes. The mentioned .020 inchdifference in lengthof the liners and the distance between shoulders I is also indicated atH in Fig. 2.

With the jacket 5 and liners 8 machined as above, and assembled with theeasy facility permitted because the liners are smaller than the bore ofthe jacket, the assembly is subjected to sub-zero temperatures. Underactual test conditions it has been found that a two inch diameter linerhaving an eighth inch Wall, temporarily contracts to 1.9995 inches at 32F., grows to 2.002 inches at between 60 and l00 F.,

and continues to grow to 2.004 inches during the L period approximatingtwo hours or until the CO2 has completely evaporated. Under such deepfreeze, the liners are permanently grown, expanded or enlarged, asstated, and the jacket is temporarily shrunk, returning to its initialsize at room temperature. When the assembly has been restored to suchnormal temperature, an approximate .002 inch interference fit betweenthe inner diameter of the jacket and the outer diameter of the liners iseffected, the liners thereby being tightly and permanently fitted to thejacket as shown in Fig. 3.

Stress relief of the assembly may be effected with a 400 F. draw withoutchange in the assembly except to realign the molecules of the liners torelieve stress therein. The normalizing temperature may vary, asdesired.

It will be evident that the greater the differences of the machineddiameters of the jacket and liners, the easier it is to slip the linersinto the jacket. Accordingly, while higher temperatures than areobtained with solidified CO2 may be employed, the wider machiningtolerances afforded when l00 F. is used, make CO2 an at presentpreferred medium for the instant method.

4 With respect to hardness, cast iron containing 5% Ni and 2% Cr has ahardness of Rockwell C which, when the alloy is deep frozen, as above,increases to C60. This increase in hardness is a material advantage forliners and like wear parts. It will be seen that the increased Ahardness is obtained after the liners are maneeded.

chined, a further advantage since the machining is performed when theliners are relatively softer. While the metalurgy need not be discussedin detail, it may be stated that, in the iron alloy given, the nickeland chromium are the agents which harden the alloy as a casting thereofcools. No special hardening process is The increase in hardness observedunder deep freeze is thought to result from an austenitic change in thecombined carbon or iron carbide contained in the iron.

After the assembly has been restored to normal temperatures, the innerdiameter of the lined barrel is honed, to insure a uniform bore in thebarrel.

The assembly thus provided will expand and contract in the normal mannerof metals, thereby insuring retention of the tight fit that is achievedaccording to the present method.

The present method may be employed to interfit other parts than jacketsand liners, providing the inner part is formed of an alloy as abovegiven.

While we have disclosed what we now regard as the preferred method ofour invention, we do not wish to restrict ourselves to the particularmethod described but desire to avail ourselves of all modifications thatmay fall within the scope of the appended claims.

Having thus described our invention, what we claim and desire to secureby Letters Patent is:

l. A method for interfitting two metal parts one within the other thatconsists in providing the outer part with a seat that is sli htly largerthan the inner part to receive said inner part with sliding clearance,forming said inner part of a ferrous metal that includes 3.5 to 5% ofnickel and 1.4 to 2% of chromium, and subjecting the assembled parts toa sub-zero temperature that is sufficiently low enough to cause saidinner part to permanently grow to a size larger than the seatit occupiesand to tightly fit said seat.

2. A method for interfitting two metal parts one within the other thatconsists in providing the outer part with a seat that is slightly largerthan the inner part to receive said inner part with sliding clearance,forming said inner part of a ferrous metal that includes approximately5% of nickel and approximately 2 of chromium, and subjecting theassembled parts to a subzero temperature that is sufficiently low enoughto cause said inner part to permanently grow to a size larger than theseat it occupies and to tightly fit said seat.

3. A method for interfitting two metal parts one within the other thatconsists in providing the outer part with a seat that is slightly largerthan the inner part to receive said inner part with sliding clearance,forming said inner part of a ferrous metal that includes 3.5 to 5% ofnickel and 1.4 to 2% of chromium, and subjecting the assembled parts toa temperature ranging between 60 F. and I00 F. to cause said inner partto permanently grow to a size larger than the seat it occupies and totightly fit said seat.

4. A method for lining a cylindrically tubular jacket with wear andcorrosion resistant liners that consists in providing a jacket of metalthat contracts when subjected to subzero temperatures and returns to itsinitial size when returned to normal temperatures, providing a set ofliners for the jacket of a metal that expands permanently when subjectedto sub-zero temperatures, the inner diameter of the jacket and the outerdiameter of the liners having such relative size that the latterslidingly fit into the former, and then subjecting the assembly ofjacket and liners to sub-zero temperatures sufficiently low to cause theouter diameter of the liners to expand to a size greater than theinitial diameter of the jacket.

5. The method according to claim 4 in which the sub-zero temperaturesrange below 60 F.

6. The method according to claim 4 in which the liners comprise a metalincluding 3.5 to 5% nickel, 1.4 to 2% chromium and the remainder iron.

'7. A method for interfitting metal parts that consists in providing onepart with a seat that is slightly larger than the other part to receivesaid other part with sliding clearance, forming said other part of ametal that has the characteristic of permanently growing under subzerotemperatures, and subjecting the assembled parts to a sub-zerotemperature that is low enough to cause said other part to permanentlygrow to a size larger than the seat it occupies and to tightly fit saidseat.

8. A method for forming an internally lined elongated tubular assemblythat consists in providing an outer, elongated tube jacket of a metalthat temporarily shrinks under sub-zero temperature and with an innerdiameter that constitutes a seat slightly larger than the outer diameterof at least two liners, assembling said liners in the jacket by freelysliding the same into said seat, forming said liners of a ferrous metalthat includes 3.5 to 5% of nickel and 1.4 to 2% of chromium, andsubjecting the assembled parts to a sub-zero temperature that is lowenough to cause said liners to permanently grow to a diametral sizelarger than the diameter of said seat to thereby tightly fit said jacketseat.

9. A method for forming an internally lined elongated tubular assemblythat consists in providing an outer, elongated tube jacket of a metalthat temporarily shrinks under sub-zero temperature and with an innerdiameter that constitutes a seat slightly larger than the outer diameterof at least two liners, assembling said liners in the jacket by freelysliding the same into said seat, forming said liners of a ferrous metalthat includes 3.5 to 5% of nickel and 1.4 to 2% of chromium, andsubjecting the assembled parts to a sub-zero temperature that is lowenough to cause said liners to permanently grow to a diametral sizelarger than the diameter of said seat to thereby tightly fit said jacketseat, and to cause said tube jacket to temporarily shrink over theliners while the latter grow.

10. A method for interfitting two tubular metal parts one within theother that consists in casting the inner part of a ferrous metal thatincludes 3.5% to 5% of nickel and 1.4% to 2% of chromium and which metalhardens when subjected to sub-zero temperature, machining the outersurface of said part while the same is at ordinary room temperature andWhile relatively soft, forming a seat in the outer part that is slightlylarger than the machined inner part while said outer part is also atordinary room temperature, assembling the inner part with slidingclearance into the seat of the outer part, and subjecting the assembledparts to sub-zero temperature at least as low as F. to cause said innerpart, by reason of its composition, to harden and to permanently grow toa size larger than the initial size of the seat in the outer part andto, thereby, tightly fit said seat after the parts have been returned toroom temperature.

11. A method according to claim 10: the step of honing the inner surfaceof the inner tubular part to make the size of said inner surfaceuniform.

MILLARD S. BLACK. ALBERT G. SA'I'IERLA, JR.

References Cited in the file of this patent FOREIGN PATENTS NumberCountry Date 475,244 Great Britain Nov. 16, 1937 436,961 Great BritainOct. 21, 1945 OTHER REFERENCES P. 94 Steel, Nov. 6, 1944, ReclaimsUndersize Pins.

P. 445 Alloys of. Iron and Chromium, vol. Kinzel and Crafts, pub. 1937,McGraw-Hill Book Co., New York, N. Y. (Copy in Div. 3.)

P. 678 Effect of Temp. on Metals, pub. by Americ. Society of Mech. Eng,29 W. 39th St., New York, N. Y. (Copy in Div. 3.)

Cold Treating Practice With Deep Freeze, pub. in 1946 by Deep Freeze,2301 Davis St., Chicago, 111., pp. 5, 7, 24, and 30. (Copy in Div. 14.)

1. A METHOD FOR INTERFITTING TWO METAL PARTS ONE WITHIN THE OTHER THATCONSISTS IN PROVIDING THE OUTER PART WITH A SEAT THAT IS SLIGHTLY LARGERTHAN THE INNER PART TO RECEIVE SAID INNER PART WITH SLIDING CLEARANCE,FORMING SAID INNER PART OF A FERROUS METAL THAT INCLUDES 3.5 TO 5% OFNICKEL AND 1.4 TO 2% OF CHROMIUM, AND SUBJECTING THE ASSEMBLED PARTS TOA SUB-ZERO TEMPERATURE THAT IS SUFFICIENTLY LOW ENOUGH TO CAUSE SAIDINNER PART TO PERMANENTLY GROW TO A SIZE LARGER THAN THE SEAT ITOCCUPIES AND TO TIGHTLY FIT SAID SEAT.
 10. A METHOD FOR INTERFITTING TWOTUBULAR METAL PARTS ONE WITHIN THE OTHER THAT CONSISTS IN CASTING THEINNER PART OF A FERROUS METAL THAT INCLUDES 3.5% TO 5% OF NICKEL AND1.4% TO 2% OF CHROMIUM AND WHICH METAL HARDENS WHEN SUBJECTED TOSUB-ZERO TEMPERATURE, MACHINING THE OUTER SURFACE OF SAID PART WHILE THESAME IS AT ORDINARY ROOM TEMPERATURE AND WHILE RELATIVELY SOFT, FORMINGA SEAT IN THE OUTER PART THAT IS SLIGHTLY LARGER THAN THE MACHINED INNERPART WHILE SAID OUTER PART IS ALSO AT ORDINARY ROOM TEMPERATURE,ASSEMBLING THE INNER PART WITH SLIDING CLEARANCE INTO THE SEAT OF THEOUTER PART, AND SUBJECTING THE ASSEMBLED PARTS TO SUB-ZERO TEMPERATUREAT LEAST AS LOW AS -60* F. TO CAUSE SAID INNER PART, BY REASON OF ITSCOMPOSITION, TO HARDEN AND TO PERMANENTLY GROW TO A SIZE LARGER THAN THEINITIAL SIZE OF THE SEAT IN THE OUTER PART AND TO, THEREBY, TIGHTLY FITSAID SEAT AFTER THE PARTS HAVE BEEN RETURNED TO ROOM TEMPERATURE.